Tubular incandescent lamp having interlocked filament support member and envelope



Feb. 17, 197k) 3,496;4o2

- J. MARTIN TUBULAR INCANDESGENT'LAMP HAVING INTERLOCKED FILAMEN'I' SUPPORT MEMBER AND ENVELOPE Filed Feb. 9, 1968 wrrmassss INVENTOR Jack Martin BY W I &2???

United States Patent TUBULAR INCANDESCENT LAMP HAVING INTERLOCKED FILAMENT SUPPORT MEM- BER AND ENVELOPE Jack Martin, Paramus, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 9, 1968, Ser. No. 704,394 Int. Cl. H01k 1/50 U.S. Cl. 313-222 6 Claims ABSTRACT OF THE DISCLOSURE The elongated coiled-coil filament of a tubular doubleended incandescent lamp, such as a halogen-containing tungsten filament lamp, is maintained in suspended position within the envelope by an auxiliary support member that has a compressible loop portion which is seated in and interlocked with a circumferential groove formed in the inner surface of a medial segment of the envelope.

BACKGROUND OF THE INVENTION This invention relates to electric incandescent lamps and has particular reference to a tubular double-ended incandescent lamp having an axially-extending coiled filament of considerable length.

One of the problems encountered in the design and manufacture of so-called quartz-halogen type incandescent lamps is that of maintaining the filament coil in the proper position within the envelope. Lamps of this type are well known in the art and consist of a tubular quartz envelope that is sealed at both ends and contains a coiled coil filament of tungsten wire that is mounted in coaxial relationship within the envelope. Since the filaments are rather long and massive, the unsupported central portion is naturally subject to vibration and shock and tends to sag as a result of its own weight when the lamp is burned. In quartz-halogen type lamps, the degree of coil sag is quite critical because the inside diameter of the bulb is small and there is thus very little clearance between the coil barrel and the inner walls of the envelope. If the filament sag becomes excessive, the incidence of lamp failure due to envelope blackening and envelope bulging increases. In extreme cases, the filament may even touch the envelope wall and create a situation where the envelope may crack and trigger a violent failure.

It is accordingly necessary to provide an auxiliary support member or other suitable means in such lamps to maintain the filament in suspended position relative to the enclosing envelope walls during the useful life of the lamp. Heretofore, this was achieved by making the coiledcoil filament in two segments or sections and then joining such sections by a tie wire having an enlarged arcuate portion that seats against the smooth inner surface of the envelope and thus provides the desired filament-supporting action. Tubular lamps having such bisectional coiledcoil filaments and various types of interconnecting support-tie wire members are shown and described in U.S. Patent Nos. 3,194,999 and 3,195,000.

Another approach to the problem has been to utilize an elongated harness-type support wire having a pair of spaced loop portions that engage the envelope walls and are joined by a yoke portion that is coupled to a filament turn, or to employ a spud-wire type of support member that is embedded in the envelope walls (or anchored in protruding dimples) and includes a pair of rods that straddle an uncoiled medial segment of the filament. Auxiliary support structures and sectionally-wound coiled filaments of the foregoing types are disclosed in U.S. Patent Nos. 3,173,051 and 3,286,116, respectively. In more recently ice issued U.S. Patent No. 3,333,139 the auxiliary support consists of a length of wire that is hooked around a filament turn and has its opposite end embedded in the tipped-off protruding segment of the vitreous exhaust tu e.

It is accordingly the general object of the present invention to provide an auxiliary support means for the filament of a tubular incandescent lamp which will maintain the filament in suspended position within the envelope and which can be manufactured and locked firmly in place within the envelope in a simple and inexpensive manner.

Briefly, the aforesaid objects and other advantages are achieved by providing a circumferential recess or groove in a medial portion of the lamp envelope and then inserting into the envelope a wire support member of spiral configuration that has a compressible arcuate portion Which slips into the groove and thus locks the support in the desired position in the envelope. The wire support member has a laterally-extending leg portion that is terminated by a loop which encircles the barrel portion of the coiled-coil filament and restricts its movement in the event it begins to sag or vibrate when the lamp is in use. Alternatively, the inner end of the aforesaid leg portion is formed into a hook that is coupled to a secondary turn of the coiled-coil filament. Thus, the required intermediate support of the suspended filament is achieved without the use of complicated support members or a member that is embedded in the sealed exhaust tip, which operation is awkward and complicates the tipping-off process. Moreover, the expense and additional fabricating steps involved in making the filament in two sections and then joining them together during lamp assembly are completely eliminated.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIGURE 1 is a side elevational view, partly in section, of a tubular incandescent lamp embodying the present invention;

FIG. 2 is an enlarged cross-sectional view through the center of the lamp and the associated support member along the line IIII of FIG. 1;

FIG. 3 is a longitudinal sectional view of the central segment of another tubular incandescent lamp having an alternative form of auxiliary support member; and,

FIG. 4 is a cross-sectional view of the aforementioned alternative embodiment along the line IV-IV of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS While the present invention can be used with advantage in various types of incandescent lamps and similar devices that contain an elongated incandescible element that requires auxiliary support means, it is especially adapted for use in conjunction with double-ended tubular incandescent lamps and has accordingly been so illustrated and will be so described.

In FIGS. 1 and 2 there is shown a 400 watt volt T4 halogen incandescent lamp 5 consisting of a tubular quartz envelope 6 that contains an elongated filament 8 which is suspended in coaxial position within the envelope and attached to inner lead conductors 10 embedded in press seals 11 formed at each end of the envelope. In accordance with standard lamp-making practice, the inner leads 10 are electrically connected to intermediate foil conductors 12 which are also embedded in the press seals 11 along with the attached ends of suitable outer leads 14. The protruding ends of the outer leads 14 are joined to metal discs or buttons 16 which serve as the lamp contacts.

Refractory sleeves 18 are slipped over the disc con- :acts 16 and outer leads 14 and fastened to the ends of he respective seals 11 by suitable cement, as shown in FIG. 1.

The filament 8 is of coiled-coil construction and is fabricated by winding a length of tungsten wire of the proper diameter into a first helix consisting of evenlyspaced primary turns, and then coiling this first helix a second time to provide a larger helix consisting of a series of much larger secondary turns 9 that are also evenly spaced. The envelope 6 is evacuated and filled with a predetermined amount of a halogen gas (such as iodine or bromine) and a suitable inert gas (such as argon, krypton, or xenon) through a centrally located exhaust tube 7, which is then tipped off in the usual manner. The halogen gas serves as a getter during lamp operation which redeposits vaporized tungsten back onto the filament and thus prevents bulb blackening in the well known manner. An iodine-cycle lamp of this type is described in US. Patent No. 2,883,571 issued to Fridrich et al.

In accordance with the present invention, the coiledcoil filament 8 is retained in its suspended position within the envelope 6 by an auxiliary filament support member 22 consisting of a resilient wire spiral that has a compressible major loop portion 23 (clearly shown in FIG. 2) of circular configuration which is seated and locked within a suitable recess, such as a circumferential groove 24, formed in the inner wall of the envelope at approximately its midpoint. As shown more particularly in FIG. 1, the groove 24 is made by deforming the medial portion of the envelope 6 in such a manner that the envelope wall bulges outwardly to form an interior circumferential indentation and an exterior protruding rib or head 26. Such deformation of the envelope 6 is readily achieved by heating the intermediate segment which is to be deformed and, after the quartz has become plastic, axially compressing the envelope to cause the softened medial portion to bulge outwardly. This deforming operation is, of course, accomplished during the manufacture of the envelope 6 before the filament 8 or any of the lead-in conductor assemblies are inserted.

As shown in FIG. 2, the spiral auxiliary support member 22 has a laterally-extending leg portion 28 that joins the major loop portion 23 with a minor loop portion 29 that is also of circular configuration and is larger in diameter than the outside diameter of the barrel of the coiledcoil filament 8. The loop 29 is preferably initially concentric with, and accordingly spaced from, the coil barrel, as illustrated. Thus, if the filament 8 sags as the lamp burns it will contact and be constrained by the inwardlydisposed minor loop 29. The minor loop 29, in addition to preventing excessive filament sag and the dangers of envelope bulging and possible subsequent sudden rupture and failure, restricts the lateral movement of the suspended filament 8 and dampens any vibrations which may develop while the lamp is in use. This construction is, accordingly, especially adapted for use in rough service lamps designed for lighting applications where the lamp will be subjected to vibration and shock.

While the spiral auxiliary support member 22 can be made from any suitable resilient refractory metal (such as molybdenum or the like) which will impart the necessary degree of compressibility to the outer loop 23 to permit it to spring into and become locked in the groove 24, it is of course made of tungsten in the case of halogen-containing incandescent lamps.

FIGS. 3-4 EMBODIMENT In FIGS. 3 and 4 there is shown another lamp embodiment 5a wherein the tubular envelope 6a is provided with an interior circumferential groove 24a and a modified form of auxiliary filament support member 22a having a large outer loop 23a that is compressively locked within the groove in the same manner as described above in connection with the FIGS. 1 and 2 embodiment. However, according to this form of the invention the laterally-extending leg 28a is terminated by a hook 30 that is looped and closed around one of the secondary turns 9a of the coiled-coil filament 8a and thus holds the coil barrel in the desired coaxial position within the envelope 6a. Since it would be rather awkward to insert the support member 22a into the envelope 6a first and then insert the filament 8a and close the hook 30 around one of its secondary turns, it is preferably in this embodiment to couple the support 28a with the filament 8a prior to the insertion of the latter and then lock the attached support 28a in place within the groove 24a by means of a suitable tool as the support-filament assembly is being placed within the envelope.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that a very simple and inexpensive means for supporting the medial portion of a coiled-coil filament in suspended position within a tubular double-ended incandescent lamp has been provided. The combination of the circumferential groove in the inner wall of the bulb and a compressible spiral support member provides a very rugged and shock-resistant lamp without requiring any modification whatsoever in the structure of the filament or interference with the tipping-off of the exhaust tube to anchor the support therein.

While several embodiments have been illustrated and described, it will be appreciated that various modifications in both the shape and arrangement of the recess and support member can be made without departing from the spirit and scope of the invention. For example, a series of spaced but circumferentially-disposed recesses of pockets in the inner wall of the envelope and a wire support with a non-circular outer loop having a corresponding number of bights or angled bends arranged to interlock with the pockets can be used.

Photometer tests have shown that the deformed medial portion of the envelope having the groove and protruding bead does not block any of the light or cause any aberration in the light-distribution pattern of the lamp. This is an obvious advantage in lighting applications where the lamp is used in an optical system or in conjunction with a reflector.

I claim as my invention:

1. In an electric incandescent lamp, the combination of;

a tubular envelope that is sealed at both ends and has and intermediate portion with an interior circumferentially-extending recess,

an elongated incandescible filament extending longitudinally of and suspended within said envelope, and

an auxiliary filament-support member having (1) a compressible portion that is seated in and interlocked with said circumferential recess and (2) an inwardly-disposed portion that encircles an intermediate part of the filament and is adapted to restrict the lateral movement thereof.

2. The combination set forth in claim 1 wherein;

said recess comprises a groove that extends around substantially the entire circumference of said envelop, and

th compressible portion of said auxiliary filament-support member is of arcuate configuration.

3. The combination set forth in claim 1 wherein;

said filament comprises a helical coil that is wound from a single piece of refractory metal wire and is attached to lead-in conductors anchored in the sealed ends of said envelope,

said envelope is of circular cross-section,

said auxiliary filament-support member comprises a length of resilient refractory metal wire that is formed into a spiral having a major loop portion and minor loop portion that are joined by a laterally extending leg portion, and

the major loop portion of said spiral support member is seated in said groove and the minor loop portion encircles a part of said filament.

4. The combination set forth in claim 3 wherein; minor loop portion of said spiral support member comsaid lamp comprises a halogen-incandescent lamp, prises a hook that is closed around a secondary turn of said filament comprises a coiled-coil helix of tungsten said coiled-coil filament.

Wire that is coaxially suspended within said envelope, said spiral auxiliary filament-support member is com- 5 References C t plpsed fof tufngstenl wire and the bajorlloop cportion UNITED STATES PATENTS t ereo is o circu ar configuration and ocate at approximately the center of said envelope and filament. 1983362 12/1934 Ge'ger et 313 271 X 5. The combination set forth in claim 4 wherein the JAMES W. LAWRENCE, Primary Examiner minor loop portion of said spiral support member is of 10 circular configuration and larger than the coil barrel of PALMER DEMEO Assistant Exammer said filament and, initially, is disposed in substantially con- U S Q X R centric spaced relationship therewith.

6. The combination set forth in claim 4 wherein the 3l3-220, 223, 279 

